Method of producing a cover member for a safety air-cushion

ABSTRACT

A cover member for a safety air-cushion device is made up of a bag-shaped outer laminate of high density polyurethane foam, and a bag-shaped inner laminate of low density polyurethane foam which is integral with the outer laminate, the inner laminate being made by pouring the fluidized foamable material into a mold after solidification of the other fluidized foamable material having been poured into the mold for the formation of the outer laminate.

This is a divisional application of application Ser. No. 746,713, filedDec. 2, l976 now U.S. Pat. No. 4,120,516.

The present invention relates in general to a method of producing asafety air-cushion device for protecting an occupant of a vehicle duringa vehicle collision, and more particularly to a cover member forsubstantially covering the air-cushion device proper in a dormantcondition in order that the air-cushion device proper should not bedamaged by accidental striking by the occupant's body and/or appendage.The present invention is further concerned with a method of producingthe above-mentioned cover member.

It is well known in the art that each of the cover members for suchair-cushion devices is constructed to have at least one easily breakableportion or at least one cut portion in order that the cover member ispositively broken by the expansion of the air-cushion proper so as toallow the air-cushion proper to quickly get out from the cover memberfor the full expansion in case of a vehicle collision. On the contrary,the cover member should not be broken nor removed from its originallyset position even when subjected to violent vibrations or shocks whichare made by causes other than the expansion of the air-cushion.

In regard to the selection of material forming such a cover member, itis necessary that the material should have low density, low costproductivity and good colourability. Especially, for safety's sake, thematerial should not generate harmful gases or produce dangerous rigidcrushed pieces when broken.

Hitherto, some of such cover members have been made up of two layers ofdifferent plastic materials. For example, the top side layer for thecover member is made of a rigid plastic laminate, such as PVC resin(polyvinyl-chloride resin) or ABS resin (acrylonitrile-butadiene-styreneresin), and the back side layer of the cover member is made of a foamedpolyurethane laminate which is adhered to the inside surface of therigid plastic laminate. In this case, however, when a temperatureapplied to such combined laminates of the cover member as a result ofthe curing operation and/or the exothermic reaction of the fluidizedpolyurethane material reaches a certain value, the laminates aresubjected to deformation causing unwanted variations in the respectivethicknesses thereof. In addition, because the flexibility of the PVCresin or the ABS resin for the top side layer is remarkably lowered in acold condition, many cracks may appear in such layers in a very coldcondition even when the cover member is subjected to only slight shocks.Besides, the vacuum forming process applied to the formation of therigid plastic laminates is likely to induce occurrence of someshrinkages on the surface of them and of ill-balanced thicknesses of thelaminates, thereby badly affecting the appearance of the cover member,unwantedly. Furthermore, when such laminates are used in the vehicle,certain amounts of plasticizers contained therein evaporate in thevehicle compartment thus causing a dangerous fogging phenomenon.

Some cover members have been made of so-called integral skinpolyurethane laminates. As is well known, the integral skin polyurethanelaminate is produced by a so-called single shot molding process and hasa body the density of which is continuously decreased from the surfaceportion thereof toward the inner portion thereof. However, in this case,it is very difficult to provide an article having a well finishedsurface which promotes the exact formation of the cut portion because ofemploying the complicated single shot molding process. In reality, bysuch molding process, there have been produced many substandard articleshaving very rough surfaces. One of the methods for solving theabove-mentioned drawbacks on the integral skin polyurethane laminate isto allow the inner portion of the article to have higher density, forexample, ranging from about 0.4 g/cm³ to 0.8 g/cm³. However, in thiscondition, the weight of the article and thus the total weight of thecover member are unwantedly increased inevitably. When the article isproduced to have high density gradient for the purpose of reducing theweight thereof, not only partial shrinkages appear on the article tolower the appearnace thereof, but also the mechanical strength of thearticle is considerably decreased. In this case, therefore, somereinforcements, such as metals, embedded within the article are requiredto prevent the cover member from being cracked into several pieces uponthe breakage of the cover member. However, this procedure will alsoinduce some drawbacks, such as increase in weight of the cover member,the fear of permanent deformation of the cover member due to thedeformation of the plastical reinforcements, and the danger of the rigidreinforcements being partially exposed from the cover member upon thevehicle collision.

Therefore, the present invention provides an improved method forproducing a cover member for the air-cushion device, which can eliminatethe several drawbacks encountered in the conventional cover membersmentioned above.

It is an object of the present invention to provide an improved covermember which is made up by a bag-shaped inner polyurethane foam laminateof low density and a bag-shaped outer polyurethane foam laminate of highdensity, the inner polyurethane foam laminate being made by injectingthe fluidized foamable urethane material into a mold aftersolidification of the other foamable urethane material having beenpoured into the mold for the formation of the outer polyurethane foamlaminate.

It is another object of the present invention to provide an improvedcover member, having at least one cut or slit portion which is used forreadily and positively breaking the cover member, when the expansion ofthe air-cushion occurs, to quickly get the air-cushion out of the covermember for full expansion of the air-cushion in a case of the vehiclecollision.

It is still another object of the present invention to provide animproved molding method for the production of the cover member mentionedabove.

Other objects and advantages of the present invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings, in which

FIG. 1 is a sectional view of the cover member according to the presentinvention and

FIGS. 2A to 2F are sectional views depicting the production process ofthe cover member according to the present invention.

Referring to the FIG. 1, there is illustrated an improved cover member10, according to the present invention, which substantially covers anair-cushion 12 in a dormant condition as illustrated in a solid line.The cover member 10 comprises a bag-shaped inner laminate ofpolyurethane foam 14 arranged to substantially hold in it the expansibleair-cushion 12. The foamed inner laminate 14 (which will be referred toas inner laminate hereinafter) is formed to have a density ranging fromabout 0.2 g/cm³ to about 0.5 g/cm³ and is formed at the closed endportion thereof with two trapezoidal slits 16 which extend through theclosed end portion. Covering the outer surface of the inner polyurethanelaminate 14 is an outer laminate 18 of polyurethane foam (which will bereferred to as outer laminate hereinafter) which has a density rangingfrom about 0.5 g/cm³ to about 1.2 g/cm³. As shown, the closed endportion of the outer laminate 18 is formed with two grooves 20 which arearranged to open to the before-mentioned slits 16 to form twosubstantially V-shaped cut portions in the cover member 10. Preferably,each of the V-shaped cut portions is formed to define a wall thicknessof about 0.4 mm between the extending end thereof and the outer surfaceof the outer laminate 18, the wall thickness being indicated by theletter T in FIG. 1. Although in this drawing, two cut portions areprovided, only one cut portion may be formed in the cover member 10 aslong as the cover member 10 is readily and positively broken by theexpansion of the air-cushion 12 in the case of the vehicle collision.Designated by the reference numeral 22 are metal supports which have oneof their ends firmly disposed in the inner laminate 14 at positionsadjacent an opening 24 of the cover member 10. The other ends of themetal supports 22 are tightly connected to the vehicle body (not shown).With this construction, when the air-cushion 12 is suddenly expanded inresponse to the vehicle collision to thus strongly push the innersurface of the inner laminate 14 outward, the cover member 10 is openedalong the cut portions thus allowing the air-cushion 12 to get out fromthe cover member 10 for the full expansion of the air-cushion 12.

In regard to the molding method of the above-mentioned cover member 10,the following procedures will be required. For facilitation, thefollowing explanation will be made with reference to FIGS. 2A to 2F.

Referring to FIG. 2A, a first fluidized foamable urethane material 18(which will be referred to as first fluidized urethane material,hereinafter) is poured or injected into a female mold 26 having adesired-shaped recess the contour of which is similar to the outline ofthe outer laminate 18 shown in FIG. 1. Just after the viscosity of thefirst fluidized urethane material 28 proceeds to a degree beyond 10,000cps, a first male mold 28 having an outer surface with two firstprojections 30 extending outwardly is inserted into the recess of thefemale mold 26 so as to give an active pressure above 500 g/cm² to thefirst fluidized urethane material 18 as seen from FIG. 2B, the insertionof the first male mold 28 into the female mold 26 should be made so thatthe leading ends of the projections 30 do not reach the inner surface ofthe recesses of the female mold 26. After solidification of the firsturethane material 18 the first male mold 28 is removed from the femalemold 26 leaving the solidified polyurethane foamed resin 18 in therecess of the female mold 26. With these procedures, the outerpolyurethane foamed laminate 18 is prepared with a uniform density andtwo cut portions 20 at the inner surface portion thereof as is seen fromFIGS. 2C. Of course, before pouring the first fluidized urethanematerial 18 into the female mold 26, consideration for the selection ofthe urethane materials and the operating parameters of the urethanepouring machine should be given by the operator in order that thesolidified outer foam laminate 18 will have the density ranging fromabout 0.5 g/cm³ to about 1.2 g/cm³.

Then, as is understood from FIG. 2D a second male mold 32 having anouter surface with two second projections 34 extending outwardly isinserted into a bore having been formed in the solidified outerpolyurethane foam laminate 18, in such manner that the leading ends ofthe second projections 34 are received in the two cut portions 20 of theouter foam laminate 18 while providing a certain clearance 36 betweenthe inner surface of the outer foam laminate 18 and the outer surface ofthe second male mold 32. Before the second male mold 32 is inserted intothe bore of the outer laminate 18, suitable numbers of metal supports 22are releasably fixed to the second male mold 22. These metal supports 22are fixed to such positions that they are brought into contact with theinner surface of the outer laminate 18 adjacent the opening of the sameupon fitting of the second male mold 32 to the bore of the outerlaminate 18. This will be understood from FIG. 2D. Then as isillustrated in FIG. 2E a second fluidized foamable urethane material 14(which will be referred to as second fluidized urethane materialherinafter) is poured or injected into the before-mentioned clearance 36formed between the inner surface of the outer laminate 18 and the outersurface of the second male mold 32. After solidification of the secondurethane material 14, the second male mold 32 is released or removedfrom the solidified second foam resin 14, leaving the metal supports 22in the solidified second foam resin 14. With this, the innerpolyurethane foam laminate 14 is made. Finally, the female mold 26 isreleased from the combined outer and inner polyurethane foam laminates18 and 14. It is to be noted that the materials and the operatingparameters of the urethane pouring machine for the second fluidizedurethane material 14 are selected and controlled so that the solidifiedinner polyurethane foam laminate 14 will have the density ranging fromabout 0.2 g/cm³ to about 0.5 g/cm³. With these procedures, the combinedarticle as shown in FIG. 2F can be produced.

EXAMPLE

The following Tables I and II show the respective properties of thesolidified outer and inner polyurethane foam laminates 18 and 14 whichwere produced by employing the above-described molding method.

                  Table I                                                         ______________________________________                                        Property of the Solidified Outer                                              Polyurethane Foam Laminate (18)                                                               Curing time 17 seconds                                                        Weight 176 g                                                  ______________________________________                                        Measuring temperature (°C.)                                                              -40     -20     +20   +80                                   Mechanical property                                                           Tensile strength (Kg/cm.sup.2)                                                                  309     200     124   48                                    Elongation (%)    330     340     380   230                                   Flexural modulus at 50%                                                       compression (Kg/cm.sup.2)                                                                       135     65      37    28                                    Tear resistance (Kg/cm)                                                                         106     69      31    20                                    Hardness of Shore . D                                                                            43     35      32    27                                    Hardness of Shore . D of a                                                    conventional half-hard PVC                                                                       74     68      52    26                                    sheet of 0.8 mm in thickness                                                  ______________________________________                                    

                  Table II                                                        ______________________________________                                        Property of the Solidified Inner                                              Polyurethane Foam Laminate (14)                                                               Curing time 20 seconds                                                        Weight 84 g                                                   ______________________________________                                        Measuring temperature (°C.)                                                              -40     -20     +20   +80                                   Mechanical Property                                                           Tensile strength (Kg/cm.sup.2)                                                                  98      82      22    14                                    Elongation (%)    71      100     190   69                                    Flexural modulus at 50%                                                       compression (Kg/cm.sup.2)                                                                       94      66      12    13                                    Tear resistance (Kg/cm)                                                                         29      26      11     6                                    ______________________________________                                         *The combined article consisting of these laminates 18 and 14 is              considerably lighter than an article made of the beforementioned integral     skin polyurethane foam.                                                  

According to our several practical experiments, the following resultswere further obtained.

(1) The formation of the cut portions in the cover member 10 wasaccurate, so that the dimensional uniformity of thickness of the walldefined by the extending end of each cut portion and the outer surfaceof the outer polyurethane foam laminate 18 is considerably improved.

(2) The unwanted cracks in the cover member 10 did not appear even whenthe subject cover member was left in a very cold condition for a longtime.

(3) The wear proof of the outer foam laminate 18 was far better than theintegral skin foam mentioned before.

(4) The dangerous fogging phenomenon did not occur even when the covermember 10 was used in a motor vehicle cabin. This is because theurethane resin does not contain much plasticizers.

(5) It was easy to increase the reaction rate of each of the urethanematerials since these materials are individually used for the respectiveformations of the outer and inner polyurethane foam laminates 18 and 14.Thus, the projection rate and thus the production efficiency of thecover member were remarkably increased. More specifically, each covermember of the present invention was produced every 6 to 8 minutes whilethe conventional cover member such as made of the integral skinpolyurethane foam took 15 to 20 minutes for the formation thereof.

(6) The cover member of the subject invention was made with a wellfinished outer surface, more specifically, without pin holes. This meansthat painting of the outer surface of the cover member is readilyachieved even when a light color paint is used. In reality, in theconventional cover member of the integral skin polyurethane foam, onlyblack paint is used since the outer surface of it is very rough.

What is claimed is:
 1. A method of producing a two-layered polyurethanefoam cover member for an expansible air-cushion in a dormant condition,comprising in steps:(a) pouring a first fluidized formable urethanematerial into a female mold; (b) preparing a first male mold which hasat least one first projection on its outer surface; (c) inserting saidfirst male mold into said female mold and setting said first male moldin the female mold in such a manner that a certain clearance which is tobe filled with said first fluidized foamable urethane material is formedbetween an outer surface of said first male mold and an inner surface ofsaid female mold and that said first projection is prevented fromreaching the inner surface of said female mold; (d) removing said firstmale mold from said female mold upon completion of solidification ofsaid first fluidized foamable urethane material, while leaving thearticle of the urethane foam in said female mold; (e) preparing a secondmale mold which has at least one second projection on its outer surface;(f) inserting said second male mold into said female mold and settingsaid second male mold in said female mold in such a manner that acertain clearance is defined between an inner surface of said article ofthe urethane foam and an outer surface of said second male mold and thatthe leading end of said second projection is received in a groove whichhas been formed, upon the step "d", at the inner surface of said articleof the urethane foam; (g) pouring a second fluidized foamable urethanematerial into said clearance; and (h) removing said second male moldfrom said female mold when solidification of said second fluidizedfoamable urethane material is completed.
 2. A method as claimed in claim1, further comprising, before the step "f";(i) removably fixing at leastone metal support to said second male mold so that when the step "f" isaccomplished, said metal support is positioned adjacent an entrance of abore defined by said article of the urethane foam, and when the step "h"is accomplished, said metal support is embedded in the final product ofthe urethane foam.
 3. A method as claimed in claim 1, in which saidarticle of the first urethane foam has a density ranging fromapproximately 0.5 g/cm³ to approximately 1.2 g/cm³, and the product ofsaid second fluidized foamable urethane material has a density rangingfrom approximately 0.2 g/cm³ to approximately 0.5 g/cm³.
 4. A method asclaimed in claim 1, in which the step "c" is initiated just after theviscosity of said first fluidized foamable urethane material in saidfemale mold proceeds to a degree beyond 10,000 cps.
 5. A method asclaimed in claim 4, further comprising, before the step "d", (j)applying a pressure above 500 g/cm² to said first fluidized foamableurethane material which fills the certain clearance between the firstmale mold and the female mold.